In the high-pressure fuel pump assembly mechanism described in EP-1519033A2, a holder (46) having an external cylindrical surface portion (46) fitted to a mounting hole (48) formed in an engine. In addition, the assembly mechanism is configured such that a plunger seal member is held by an internal cylindrical surface portion of the holder (46).
In accordance with the assembly mechanism, the outer cylindrical surface portion and the inner cylindrical surface portion can be formed by machining a single member. Therefore, the respective centers of the external cylindrical surface portion and of the inner cylindrical surface portion can be machined coaxially with each other.